I'm mystified by the enormous gap between the open source solutions and Nomachine, both in the technical and usability areas. The open source solutions are sadly terrible; those who aren't convinced, just try Nomachine.
It's puzzling because solutions like X2Go (which I found to be the most usable) rely on older NX protocol versions (v3 was open), but still, they have terrible performance. This means that in the last 10 years, there has been no virtually development in the open source remote desktop field.